PHP Ds\PriorityQueue peek() Function

The Ds\PriorityQueue::peek() Function in PHP is used to get the value present at the front of a PriorityQueue.

Syntax:

mixed public Ds\PriorityQueue::peek ( void )

Parameters: This function does not accepts any parameters.

Return Value: This function returns the value present at the front of this PriorityQueue. The return type of the function is mixed and depends on the type of value stored in the PriorityQueue.

Exception: This function throws an UnderflowException if the PriorityQueue is empty.

Below programs illustrate the Ds\PriorityQueue::peek():

Program 1:

<?php

// Declare new PriorityQueue
$pq = new \Ds\PriorityQueue();

// Add elements to the PriorityQueue
$pq->push("One", 1);
$pq->push("Two", 2);
$pq->push("Three", 3);

echo "PriorityQueue is: \n";
print_r($pq);

// Get element at the front
echo "\nElement at front is: ";
print_r($pq->peek());

?>

Output:

PriorityQueue is: 
Ds\PriorityQueue Object
(
    [0] => Three
    [1] => Two
    [2] => One
)

Element at front is: Three

Program 2:

<?php

// Declare new PriorityQueue
$pq = new \Ds\PriorityQueue();

echo "PriorityQueue is: \n";
print_r($pq);

// Get element at the front
echo "\nElement at front is: ";
print_r($pq->peek());

?>

Output:

PHP Fatal error:  Uncaught UnderflowException

Reference: http://php.net/manual/en/ds-priorityqueue.peek.php